A conventional electrical nail gun is powered by AC power which requires a cord connected between the nail gun and a receptacle or a power supply unit. However, the cord might be tangled by object and pulls the nail gun off from the user's hand. This could lead to a dangerous result. Therefore, a DC-powered nail gun resolves all the shortcomings of the conventional electric nail gun and only a battery pack is needed which is usually connected to an underside of the handle of the nail gun. The battery pack provides necessary electric power to the nail gun so that the nail gun can be freely moved without being tangled. The power of the battery pack drives a disk which has a protrusion and a push rod is then moved backward and a spring mounted on the push rod is compressed so as to generate the needed force to shoot the nails. In a specific condition, when the disk is rotated an angle and the spring is compressed, the battery pack runs out while the push rod is still in that position where the force is stored by the spring. The user then replaces a new battery pack to the nail gun. The new battery pack provides sufficient electric power and the disk then rotates from the position when the previous battery pack runs out. This might cause a sudden shoot when the nail gun is not aimed toward the object to he nailed.
The present invention intends to provide a protection device that shift a switch away from the protrusion of the disk when replacing a new battery pack so that no sudden shoot may happen.